Detailed explanation of php magic variable usage examples, detailed explanation of php magic examples_PHP tutorial

Detailed explanation of php magic variable usage examples, detailed explanation of php magic examples

The example in this article describes the usage of php magic variables, among which __DIR__ is new in php5.3 and is shared with everyone for your reference. The specific usage analysis is as follows:

System constants

__FILE__ current file name
__LINE__ Current line number
__FUNCTION__ Current function name
__CLASS__ current class name
__METHOD__ The method name of the current object

Detailed analysis

1. __FILE__

The full path and file name of the file. If used within an included file, returns the name of the included file. Since PHP 4.0.2, __FILE__ always contains an absolute path (or the resolved absolute path in the case of a symbolic link), whereas versions before that sometimes contained a relative path.
PHP constant dirname(__file__)
__FILE__: Known as PHP magic constant, returns the full path and file name of the currently executing PHP script, including an absolute path

1) The dirname(__FILE__) function returns the path where the script is located. Update network
For example, the file b.php contains the following content:

Copy code The code is as follows:

$basedir = dirname(__FILE__);
echo $basedir
//An absolute path to the file will be printed on the page!
?>

The test I did got the result: E:websiteothertestcms
This is equivalent to the usage of server.mappth in asp
If b.php is referenced by a.php file require or include in other directories. The content of the variable $basedir is still the path to the folder where b.php is located. Instead of becoming the directory where the a.php file is located.

2) dirname(__FILE__) generally returns a directory structure from the current directory where the file is located to the system root directory.
The current file name is not returned. dirname(__FILE__) may also return a . (current directory) [The reason is that the b.php file is in http.conf or the default WEB directory of the PHP configuration development environment

Copy code The code is as follows:

/**
In your public configuration file, set your root directory so you don't have to worry about moving frequently.
*/
define('ROOT_PATH', dirname(__FILE__) . DIRECTORY_SEPARATOR);
echo ROOT_PATH;
echo "
";
echo __FILE__;
echo "
";
echo dirname(__FILE__);
echo "
";
echo dirname(dirname(__FILE__));
?>

2. __LINE__

The current line number in the file. This variable is quite useful when debugging errors. At other times, it is of little use. It is purely a personal opinion.

Copy code The code is as follows:

echo __LINE__; //Display, the line number where __LINE__ is located
?>

3. __CLASS__
The name of the class, the results returned by PHP5 are case-sensitive

Copy code The code is as follows:

class base_class
{
function say_a()
{
echo "'a' – said the " . __CLASS__ . "
";
}
function say_b()
{
echo "'b' – said the " . get_class($this) . "
";
}
}
class derived_class extends base_class
{
function say_a()
{
parent::say_a();
echo "'a' – said the " . __CLASS__ . "
";
}
function say_b()
{
parent::say_b();
echo "'b' – said the " . get_class($this) . "
";
}
}
$obj_b = new derived_class();
$obj_b->say_a();
echo "
";
$obj_b->say_b();
?>

The result is:

Copy code The code is as follows:

'a' – said the base_class
'a' – said the derived_class
'b' – said the derived_class
'b' – said the derived_class

Sometimes, we can use get_class instead of __CLASS__

4. __FUNCTION__ and __METHOD__

__FUNCTION__: function name, the result returned in php5 is case-sensitive
__METHOD__: The function name in the method, the result returned in php5 is case-sensitive
Both are the names of the acquisition methods. What's the difference?

Copy code The code is as follows:

class test
{
function a()
{
echo __FUNCTION__;
echo "
";
echo __METHOD__;
}
}
function good (){
echo __FUNCTION__;
echo "
";
echo __METHOD__;
}
$test = new test();
$test->a();
echo "
";
good();
?>

Return result:
a
test::a
good
good
Compared with an isolated function, both can extract the function name. There is no difference. If it is a method in a class, __FUNCTION__ can only extract the method name of the class, while __METHOD__ can not only extract the method name, but also the method name. class name

5. __DIR__

The directory where the file is located. If used within an included file, returns the directory where the included file is located. It is equivalent to dirname(__FILE__). Directory names do not include the trailing slash unless they are the root directory. (New in PHP 5.3.0)
If you want to use __DIR__ in versions prior to 5.3, you can do this

Copy code The code is as follows:

if(!defined('__DIR__')) {
$iPos = strrpos(__FILE__, "/");
define("__DIR__", substr(__FILE__, 0, $iPos) . "/");
}
?>

6. __NAMESPACE__

The name of the current namespace (case sensitive). This constant is defined at compile time (new in PHP 5.3.0)

7. __STATIC__

When you call a static method of a class, the class name is returned, case-sensitive. If called in inheritance, the inherited class name can be returned regardless of whether it is defined in inheritance.

Copy code The code is as follows:

//php5.3
class Model
{
public static function find()
{
echo __STATIC__;
}
}
class Product extends Model {}
class User extends Model {}
Product::find(); // "Product"
User::find(); // "User"
?>

Additional: Magic method in php

__construct() When instantiating an object, this method of the object is first called.
__destruct() This method is called when an object is deleted or when the object operation terminates.
__get() is called when trying to read a property that does not exist.
__set() is called when trying to write a value to a property that does not exist.
__call() This method is called when trying to call a method that does not exist on the object.
__toString() is called when printing an object
__clone() is called when the object is cloned
__isset()
__unset()
__autoload($classname)
__sleep()
__wakeup()

I hope this article will be helpful to everyone’s PHP programming design.

http://www.bkjia.com/PHPjc/910596.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/910596.htmlTechArticleDetailed explanation of php magic variable usage examples, php magic examples detailed explanation This article describes the usage of php magic variables, among which __DIR__ It is new in php5.3 and is shared with everyone for your reference. Specific usage...